Rudolf said:
Cat gets into places where I do not want it to go and I want to set up
a detector there that will scare it away.
LOL! When I don't want my cats to go somewhere, I close a door!
Ue of IR detection will not work as people get there too.
It will, if you make some attempt to differentiate between
people-sized bits of IR, and cat-sized bits of IR.
[...]
I am after a detector that will read the ID from a distance of
a bout 1-1.5m. Reader does not have to be self-contained.
With respect Sir, it's not gonna happen. The RFID 'capsules'
they're using on animals have such a tiny antenna that it may
as well not have one at all. That is certainly the case at
the distances you're talking.
We keep a cache of assorted RFID 'chips' to show to students
during the Supply Chain Management lecture on bar codes, rfid,
etc. Some have quite large antennas - the ones that the Hong
Kong Airport Authority attach to every item of checked luggage
that flows out of the place are about 50mm x 200mm - and of
course most of that is antenna. The antenna in an animal capsule
is tiny by comparison - a small coil of copper wire.
I had to take my young bloke back to the RSPCA recently to get
his number checked (someone made a typo, got it wrong, blocked
some little old lady registering her cat up on the Central
Coast! In a system of RFID and bar codes, someone *still*
ended up manually typing a (very) long number!).
So I had a chance to have another good look-see at the RFID
readers they're using. They're a battery powered device with
a large coil antenna - a diameter in the order of 100mm at
a guess.
Common practice is to insert the capsule between the shoulder
blades. In my boy's case, it has slipped off, and down one side
of his shoulder (you can feel it under his skin) - perhaps 20-30mm
away from where you might expect it to be
That distance is enough to make it really difficult to read
his number. It takes several attempts, 'scanning' over his
shoulders with the reader pressed on his skin.
This isn't a one-off. I've seen similar difficulties with
reading on others, dogs too, in the past.
What this means for you is that it's going to be nigh-on-
impossible to get a reading of any sort at a distance of
1000-1500mm...
Having said that, you don't necessarily need a *reading*
as such. What you need to do is identify the presence of a
device that 'talks' when excited by an RF field. That's
going to be a *lot* easier (and a lot cheaper) than
understanding what it is actually talking about. I'm
assuming here that you don't need to confirm that it is
specifically *your* cat that is where you don't want it
to be???
Anyway, not needing to know the actual number means that
you get to up your 'read' distance to something like
25-50mm. Still doesn't really solve your problem, does
it.
I think back to the IR thing might be a better bet. You
*can* get the 1000-1500mm read to happen with the capsule
implanted in your cat, but there are serious health-and-
safety implications and, notwithstanding that there's nothing
ferrous about your cat, you're still going to end up with
him/her being *so* magnetically polarised that you'll have
trouble with him/her sticking to the fridge all the time!
I haven't even *touched* on the bit where RF generally is
a total black art, or the amounts of money involved in
reading RFID. You're using a micro. Go IR. A bunch of
recievers at diffent heights. If the one near the ground
is the only one lit up then its a cat or a human playing
silly-buggers who deserves to be scared away anyway
HTH,
GB